The present invention relates to an apparatus and method for diagnosing and controlling combustion in an internal combustion engine including a gas engine which is constituted so that fuel gas is mixed with air and burned in the combustion chamber thereof.
It is demanded in an internal combustion engine, particularly in a gas engine which uses clean gas such as town gas as main fuel, to sense with reliability the occurrence of knock due to misfire, flame quenching or uneven mixture in the combustion chamber and to take a measure to deal with the phenomenon without delay. Further, it is required in a gas engine, petrol engine, and diesel engine, etc. to detect positively the excessive increase of the maximum combustion pressure in the combustion chamber, i.e. the maximum cylinder pressure or the reduction of compression pressure in addition to misfire, flame quenching, or knock for maintaining the durability, stability of performance of the engine.
It is inevitable in a gas engine, petrol engine, and diesel engine, etc. that the condition of combustion in the combustion chamber is detected, diagnosed, and the ignition timing of the fuel and the fuel injection quantity are properly controlled according to the result of the diagnosis. Further, it is required that, even when something wrong occurs with the maximum cylinder pressure detector, which is the detector of the condition of combustion, there is speedy recovery from the abnormal condition and resumption of normal diagnosis and control of combustion.
Combustion diagnosis systems for detecting and diagnosing the condition of combustion in the combustion chamber of internal combustion engines are disclosed in Japanese Patent Application Publication No.2000-110652, No.11-183330, and Japanese Patent No.2712332, etc.
According to Japanese Patent Application Publication No.2000-110652, a frequency band is determined according to the now-operating parameter of the internal combustion engine, the signal component of frequencies belonging to the extraction frequency band is extracted from the detected signal of cylinder pressure by means of a filter, and knock is judged to be occurring when the extracted component exceeds a threshold value.
In Japanese Patent Application Publication No.11-183330, misfire is judged to be present when the crank angle when the value of the pressure in the detected signal from the cylinder pressure detector is maximum, i.e. the crank angle at the maximum cylinder pressure is in the range of a predetermined crank angle and at the same time the mean effective pressure calculated from the detected cylinder pressure signal is below the predetermined value.
According to Japanese Patent No.2712332, engine rotation speed is detected to monitor the change thereof, and misfire is judged to be present when engine rotation speed has gone below the predetermined value.
However, in the invention of Japanese Patent Application Publication No.2000-110652, the signal component of frequencies belonging to the extraction frequency band is extracted by a filter means, so complicated computation processing such as changing of a pass band accompanying the treatment by the filter means is necessary. Therefore, the judgement of the occurrence of knock and control thereof are complicated. Further, as the absolute value of the cylinder pressure is necessary, the accuracy of the detected cylinder pressure decreases and correct diagnosis of combustion is impossible when the output level of the cylinder pressure sensor reduces totally due to deterioration, temperature drift, failed calibration, etc. of the cylinder pressure sensor.
Also in the invention of Japanese Patent Application Publication No.11-183330, the absolute value of the cylinder pressure is necessary for the judgement of misfire, so, in an analogous fashion as mentioned above, the accuracy of the detected cylinder pressure decreases and correct diagnosis of combustion is impossible when the output level of the cylinder pressure sensor reduces totally due to the deterioration, temperature drift, failed calibration, etc. of the cylinder pressure sensor.
In the invention of Japanese Patent No.2712332, the condition of combustion in the combustion chamber is detected and diagnosed by the indirect means of monitoring the change of rotation speed of the engine, so the accuracy of combustion diagnosis is low.
Further, in any of the prior inventions, an apparatus carries out combustion diagnosis only on one item, that is knock or misfire, and therefore the cost of the apparatuses becomes expensive to provide for a plurality of diagnosis functions.
In a multi-cylinder gas engine provided with an ignition device among these internal combustion engines, combustion efficiency increases and engine performance improves by advancing the fuel ignition timing. However, knock occurs more easily due to the earlier spontaneous ignition of unburned fuel. Therefore, it is required to operate with a fuel ignition timing with which knock is evaded and the maximum engine performance is maintained.
It is required, in a multiple-cylinder gas engine like this, to carry out the combustion diagnosis and combustion control so that, through the detection of the occurrence of misfire or flame quenching with good accuracy without delay from the detected data of the cylinder pressure, the fuel ignition timing and fuel injection quantity for the cylinder in which the misfire or flame quenching is occurring are adjusted to deal with the misfire or flame quenching so as to make the smooth operation of the other cylinders possible without being affected by the cylinders in which the misfire or flame quenching is occurring.
Further, in the multi-cylinder gas engine, it is required that, when abnormality occurs to any of the cylinder pressure detecting means for detecting the combustion condition in a combustion chamber due to any failure of the detecting means, the recovery of the function of the cylinder pressure detecting means is carried out while adjusting the fuel ignition timing and fuel injection quantity of the cylinder in which the abnormality in the pressure detecting means has occurred to conditions safe against abnormal combustion. After the recovery of the function of the pressure detecting means the normal combustion control is recovered automatically, and thus the occurrence of abnormality in any of the cylinder pressure detecting means can be dealt with without stopping the operation of the engine.
Further, in the multi-cylinder gas engine, it is required that the standard values (thresholds) of diagnosis items such as maximum cylinder pressure, maximum limit pressure of knock, and permissible pressure concerning occurrence of flame quenching are adjustable to match the operation condition of the engine and a high accuracy of diagnosis of the conditions of combustion is maintained.
Further, in the multi-cylinder gas engine, it is required that the occurrence of abnormality in any of the cylinder pressure detecting means can be detected at an early stage and automatically, swift recovery of the function of the cylinder pressure detecting means from the abnormal state is possible, and the combustion diagnosis is carried out smoothly.
However, none of prior arts, including the prior invention, provides a combustion diagnosis and combustion control means which can satisfy the requirements mentioned above.
Particularly, when the information of combustion diagnosis such as misfire and flame quenching is sent to a combustion control device, the method of sending the information of a plurality of cylinders digitally through a serial wire is not desirable, for the influence of a break in the wire and noise affects the control of all of the cylinders.
For this reason, a method of parallel transmittal of each individual combustion diagnosis information between the combustion diagnosis apparatus and combustion control apparatus as shown in FIG. 32 is thought of as a fail-safe. Several kinds of category""s information (2n kinds) for each of m cylinders are necessary for sending digital signals, so 2nxc3x97m or more wires are required, which demands much expense in time and effort.
Further, in none of conventional combustion diagnosis systems of a multi-cylinder engine has there been used a display which can display always changing combustion conditions of all of the cylinders in a manner easily understandable to the worker. Because of the necessity of observing the waveform of cylinder pressure for investigating the details of abnormality of combustion, an oscilloscope must be provided for each cylinder. This not only results in a complicated display, but the connection of the combustion apparatus to each oscilloscope is difficult.
Further, the historical changes of combustion conditions of the engine can be understood by observing the result of each category of diagnosis, but as the result of diagnosis changes rapidly, it is not possible to observe the output result in time sequence.
The present invention was made in light of the problems of prior art mentioned above. An object of the invention is to provide a combustion diagnosis system of an internal combustion engine, with which combustion diagnosis such as knock, misfire, flame quenching, and excessively high cylinder pressure is possible by a single apparatus; computation processing is simple; and a highly accurate result of diagnosis is obtainable without being influenced by the changes in performance of the cylinder pressure detecting means due to the deterioration of cylinder pressure sensor, temperature drift, calibration deficiency, etc.
Another object of the invention is to provide a method and apparatus for diagnosing and controlling the combustion in an internal combustion engine with which the accuracy of diagnosis using detected cylinder pressure is improved; stable operation of the engine is possible with fuel ignition timing with which the occurrence of knock is evaded and maximum engine performance can be maintained; smooth operation of the engine is possible without being exposed to the influence by the combustion in the cylinder in which misfire or flame quenching is occurring by adjusting the combustion condition in the concerned cylinder to eliminate such abnormality; and the occurrence of abnormality in any of the cylinder pressure detecting means is detected without delay and adjustment of combustion conditions in the cylinder of which the cylinder pressure detecting means has become abnormal is made so that the function of the cylinder pressure detecting means can be recovered without stopping the engine.
A further object of the invention is to provide a combustion diagnosis system with which the control of all cylinders can be performed smoothly without being influenced by data transmitting wire break, noise, etc., when the diagnosis information such as misfire, flame quenching is sent from the combustion diagnosis apparatus to the combustion control apparatus and display.
A further object of the invention is to provide a combustion diagnosis system with which the number of wires corresponding to the number of cylinders suffices for the transmission of several kinds of information of combustion diagnosis of each of a plurality of cylinders between the combustion diagnosis apparatus and combustion control apparatus and the expense in time and effort for the connection of wires is largely saved.
A still further object of the invention is to provide a combustion diagnosis system for a multi-cylinder engine, with which always changing combustion conditions of all of the cylinders can be displayed in a manner easily understandable to an operator.
A yet further object of the invention is to provide a combustion diagnosis system for a multi-cylinder engine, with which the waveform of cylinder pressure of each cylinder for the detailed investigation of abnormality in combustion in each cylinder can be effectively displayed without using oscilloscopes for all of the cylinders.
A further object of the invention is to provide a combustion diagnosis system, with which the result of each category of diagnosis can be displayed in a manner easily understandable to the operator even when the result of diagnosis judged by a combustion diagnosis apparatus for a multi-cylinder engine is changing rapidly.
To achieve these objectives, an apparatus for diagnosing and controlling combustion of an internal combustion engine according to the present invention comprises a cylinder pressure detector for detecting the pressure in the combustion chamber, a means(step) for calculating the ratio of the maximum cylinder pressure Pp to the compression pressure or pressures P0 at one or a plurality of predetermined crank angles in the compression stroke (Pp/P0) which is the maximum pressure ratio, the pressures being determined based on the pressures detected by the cylinder pressure detector, a means(step) for comparing the maximum pressure ratio (Pp/P0) with the pressure ratios predetermined stepwise for each category of diagnosis (hereafter referred to as threshold pressure ratio) and a means (step) for diagnosing the condition of combustion such as the cylinder pressure condition in the combustion chamber by judging from the result of the comparison. Each of the threshold pressure ratios are changed as a function of the engine operating conditions including engine load, engine rotation speed, and inlet air temperature as necessary.
By the way, the means is suitable to be constructed in hardware or in software. The term xe2x80x9cstepxe2x80x9d is added in parentheses, for the means is constructed in software in the embodiment described later.
To be more specific, the apparatus comprises following means (steps):
a means(step) for calculating the ratio of the maximum cylinder pressure Pp to the compression pressure P0, P3 (hereafter represented by P0) at one or a plurality of predetermined crank angles in the compression stroke (Pp/P0), the pressures being determined based on the pressures detected by the cylinder pressure detector, and a means(step) which judges that the combustion is abnormal when the maximum pressure ratio (Pp/P0) is equal to or exceeds the predetermined maximum permissible pressure ratio Pp0 or when the number of operation cycles Nh when the maximum pressure ratio (Pp/P0) is equal to or exceeds the predetermined pressure ratio Ph1 (i.e., when Pp/P0xe2x89xa7Ph1) is equal to or exceeds the permissible number Nh0 (i.e., when Nhxe2x89xa7Nh0);
a means (step) which judges that knock has occurred in the combustion chamber when the number of cycles Sn in which said maximum pressure ratio (Pp/P0) is equal to or exceeds the predetermined permissible pressure ratio of knock Ph2 (i.e., when Pp/P0xe2x89xa7Ph2) in a plurality of cycles in the past is equal to or exceeds the permissible number Sn0 (i.e., when Snxe2x89xa7Sn0);
a means(step) which judges that misfire has occurred when the maximum pressure ratio Pp/P0 is equal to or smaller than the predetermined minimum permissible pressure ratio Pn (i.e., when Pp/P0xe2x89xa6Pn) and at the same time the combustion pressure ratio (P1/P0) is equal to or smaller than the predetermined permissible pressure ratio Pm of misfire (i.e., when P1/P0xe2x89xa6Pm);
a means (step) for calculating the ratio of the lower side pressure P2 in the combustion stroke lower than the pressure P1 at a predetermined crank angle in the combustion stroke to the pressure P0 at a predetermined crank angle in the compression stroke P2/P0; and
a means(step) which judges that flame quenching has occurred when the maximum pressure ratio is equal to or smaller than the predetermined minimum permissible pressure ratio Pn (i.e., when Pp/P0xe2x89xa6Pn), at the same time the combustion pressure ratio P1/P0 is equal to or smaller than the predetermined minimum permissible pressure ratio Pm (i.e., when Pp/P0xe2x89xa6Pm) and the combustion pressure ratio P2/P0 is equal to or larger than the permissible pressure ratio Pm1 (i.e., when P2/P0xe2x89xa7Pm1).
In the configuration described above, it is preferable that a means (step) is provided which judges that the compression pressure P0 is abnormal when the compression pressure P0 at a predetermined crank angle in the compression stroke is equal to or lower than the predetermined permissible compression pressure Pc0 (i.e., when P0xe2x89xa6Pc0).
According to the invention, combustion diagnosis of detecting the occurrences of knock, misfire, excessively high maximum cylinder pressure, or flame quenching is performed by single combustion diagnosis apparatus 100 by carrying out diagnosis using pressure ratios based on the compression pressure at a predetermined crank angle in the compression stroke, so all necessary combustion diagnoses can be performed with an apparatus of simple construction and low-cost.
As the combustion diagnosis is done using pressure ratios based on a compression pressure as described above, absolute values of cylinder pressures is unnecessary and normal diagnosis is maintained without reduction in accuracy even when the output level from the cylinder pressure detector totally decreases due to the deterioration, temperature drift, failed calibration, etc. of the cylinder pressure detector. Accordingly, the operation life of combustion diagnosis apparatus can be extended.
Further, combustion diagnosis with high accuracy is possible by using, for combustion diagnosis, the cylinder pressure signals for which filtration of only noise is done through a simple Low-pass filter by removing triggers. Therefore, complicated processing, such as a change of pass-band of the filter as has been with one of said prior arts, is unnecessary and the efficiency of operation of combustion diagnosis is enhanced.
Further, combustion diagnosis with high accuracy is possible by simple means(steps), as the combustion diagnosis is carried out directly by using only cylinder pressures detected.
Therefore, according to the embodiment, all of necessary combustion diagnoses such as knock, misfire, excessively high maximum cylinder pressure, and flame quenching are possible with simple equipment and in a simple manner, and a decrease in combustion performance of an engine can be detected with high accuracy and without delay.
The present invention is characterized in that the pressure in the combustion chamber is detected, the pressure difference xcex94P between the detected pressure P and reference pressure Pb which is the pressure at or before the beginning of compression including inlet air pressure (xcex94P=Pxe2x88x92Pb) is calculated for every crank angle, and a standardized pressure ratio which is the ratio of the pressure difference xcex94P to the pressure difference xcex94P0, i.e. xcex94P/xcex94P0, xcex94P0 being the pressure difference between the pressure P0 at one or a plurality of predetermined crank angles in the compression stroke and the reference pressure Pb (xcex94P0=Pxe2x88x92Pb), is used for the diagnosis of the combustion conditions such as the condition of cylinder pressure in the combustion chamber.
As an apparatus suited for effecting the method of diagnosing and controlling combustion is proposed an apparatus for diagnosing and controlling combustion of an internal combustion engine which is constituted such that fuel gas is mixed with air and burned in the combustion chamber/There are provided; a cylinder pressure detector for detecting the pressure in the combustion chamber, a crank angle detector for detecting crank rotation angles of the engine, a means(step) for calculating the pressure difference xcex94P between detected cylinder pressure P and the reference pressure Pb at or before the beginning of compression including inlet pressure (xcex94P=Pxe2x88x92Pb) from the cylinder pressure detected by the cylinder pressure detector for every crank angle, a means(step) for calculating standardized pressure ratio which is the ratio of said pressure difference xcex94P to the pressure difference xcex94P0, i.e. xcex94P/xcex94Po, a P0 being the pressure difference between the pressure P0 at one or a plurality of predetermined crank angles in the compression stroke and the reference pressure Pb (xcex94P0=Pxe2x88x92Pb), a means (step) for diagnosing the condition of combustion such as the cylinder pressure condition in the combustion chamber using the standardized pressure ratio xcex94P/xcex94P0, and a combustion control apparatus for controlling the combustion condition of the engine on the basis of the result of the combustion condition diagnosis outputted from the combustion condition diagnosis means (step).
According to the invention, absolute cylinder pressure is not required for the diagnosis because a standardized pressure ratio xcex94P/xcex94P0, based on the pressure difference xcex94P0 between pressure P and the pressure Pb (xcex94P0=Pxe2x88x92Pb), Pb being the pressure at or before the beginning of compression including inlet air pressure of which the fluctuation due to outside conditions such as atmospheric condition, is small during the operation of the engine. Normal diagnosis can be carried out maintaining the specified accuracy of diagnosis without reducing the accuracy even when the output level of the cylinder pressure detector is totally reduced or increased due to the deterioration thereof, temperature drift, calibration deficiency, etc.
The present invention is characterized in that the engine is stopped when the standardized cylinder pressure ratio xcex94P/xcex94P0 at the maximum cylinder pressure Pp, that is the standardized maximum pressure ratio xcex94Pp/xcex94P0, is equal to or exceeds the predetermined maximum permissible pressure ratio Pp0 (i.e., when xcex94Pp/xcex94P0xe2x89xa7Pp0), and for example, it is suitable to stop the engine when the pressure difference xcex94P0 at one or a plurality of predetermined crank angle is equal to or lower than a predetermined permissible compression pressure difference Pc0 (i.e, when xcex94P0xe2x89xa6Pc0)
It is also suitable that fuel(including the pilot fuel injected into the sub-chamber of a gas engine) ignition timing is retarded by a certain crank angle when the standardized maximum cylinder pressure ratio xcex94Pp/xcex94P0 is equal to or exceeds the predetermined maximum reference pressure ratio Psh (i.e., when xcex94Pp/xcex94P0xe2x89xa7Psh), and fuel ignition timing is advanced by a certain crank angle when the standardized maximum cylinder pressure ratio xcex94Pp/xcex94P0 is equal to or below the predetermined minimum reference pressure ratio Ps1 (i.e., when xcex94Pp/xcex94P0xe2x89xa7Ps1).
In this case, as an apparatus suited for effecting the method of diagnosing and controlling combustion, the combustion diagnosis apparatus is provided with a means (step) for comparing the standardized maximum cylinder pressure ratio xcex94Pp/xcex94P0 with predetermined maximum permissible pressure ratio Pp0. The combustion control apparatus is provided with a stopping means (step) to activate an engine stopper to halt the operation of the engine when the result of comparison in the combustion diagnosis apparatus is xcex94Pp/xcex94P0xe2x89xa7Pp0.
It is preferable in the invention that the combustion diagnosis apparatus is provided with a means(step) for comparing the standardized maximum pressure ratio xcex94Pp/xcex94P0 with the maximum value Psh of maximum reference pressure ratio and with the minimum value Ps1 of maximum reference pressure ratio. The combustion control apparatus is provided with a means(step) for retarding the fuel ignition timing by a certain crank angle when the result of the comparison is xcex94Pp/xcex94P0 greater than Psh and for advancing the ignition timing by a certain crank angle when the result of said comparison is xcex94Pp/xcex94P0xe2x89xa6Ps1.
According to the invention, by stopping the engine by allowing the combustion control apparatus to activate the engine operation stopper when a diagnosis result has been outputted from the combustion diagnosis apparatus that the standardized maximum pressure ratio xcex94Pp/xcex94P0 is equal to or exceeds the predetermined permissible maximum pressure ratio Pp0, the detection of the excessive high maximum cylinder pressure and the action to deal with that can be taken exactly without delay. Therefore, engine breakage or reduction of engine durability due to the excessive high cylinder pressure can be prevented with reliability.
Further, when the standardized maximum pressure ratio xcex94Pp/xcex94P0 is judged to be equal to or exceeds the maximum reference pressure ratio Psh, the fuel ignition timing is retarded by a certain crank angle by the combustion control apparatus, and when the standardized maximum pressure ratio xcex94Pp/xcex94P0 is judged to be smaller than the maximum reference pressure ratio Psh, the fuel ignition timing is advanced by a certain crank angle by the combustion control apparatus. Therefore, the cylinder pressure is maintained below the maximum reference pressure and the expected engine performance is maintained, resulting in suppression of increased generation of NOx due to excessively high combustion temperature.
The method of diagnosing and controlling combustion according to the present invention is characterized in that the fuel ignition timing is retarded by a certain crank angle when the standardized maximum pressure ratio xcex94Pp/xcex94P0 is equal to or exceeds the predetermined permissible pressure ratio Ph2 of knock (i.e., when xcex94Pp/xcex94P0xe2x89xa7Ph2)
For effecting the method of diagnosing and controlling combustion, the apparatus is composed such that the combustion diagnosis apparatus is provided with a means (step) for comparing the standardized maximum pressure ratio xcex94Pp/xcex94P0 with the predetermined permissible pressure ratio Ph2 of knock and judging that knock has occurred when said standardized maximum pressure ratio xcex94Pp/xcex94P0 is equal to or exceeds the permissible pressure ratio Ph2 of knock. The combustion control apparatus is provided with a means(step) for retarding the fuel ignition timing by a certain crank angle upon receipt of a judgement signal of the occurrence of knock.
According to the invention, if the result of diagnosis by the combustion diagnosis that the standardized maximum pressure ratio xcex94Pp/xcex94P0 reaches the predetermined permissible value for knock, i.e. the maximum limit of maximum cylinder pressure ratio at which the engine performance is maintained at maximum while evading the occurrence of knock, the fuel ignition timing is retarded through the combustion control apparatus. As a result, the engine performance is controlled optimally to operate with high performance in the condition just before the occurrence of knock.
According to the method of diagnosing and controlling combustion of the invention, misfire is judged to have occurred in the combustion chamber and the fuel injection for the cylinder in which misfire is judged to have occurred is shut off when the standardized maximum pressure ratio xcex94Pp/xcex94P0 is equal to or below the predetermined minimum permissible pressure ratio Pn of misfire (i.e., when xcex94Pp/xcex94P0xe2x89xa6Pn)
As an apparatus for effecting the method of the invention said combustion diagnosis apparatus is provided with a means(step) for comparing the standardized maximum pressure ratio xcex94Pp/xcex94P0 with the predetermined permissible pressure ratio of misfire and judging that misfire has occurred in the combustion chamber when the standardized maximum pressure ratio xcex94Pp/xcex94P0 is equal to or smaller than the minimum permissible pressure ratio Pn of misfire. The combustion control apparatus is provided with a means(step) for cutting off the fuel injection to the cylinder in which misfire has occurred upon receipt of a judgement signal of the occurrence of misfire.
According to the invention, when a diagnosis result has been outputted from the combustion diagnosis apparatus that the number of continual cycles in which the standardized maximum pressure ratio xcex94Pp/xcex94P0 reaches the predetermined permissible pressure ratio of misfire reaches the predetermined permissible number of continual cycles, the fuel injection to the concerned cylinder in which misfire has occurred is cut off.
Therefore, the occurrence of misfire is detected with reliability and without delay and measures can be taken to deal with the situation, that is, to stop the fuel injection to the concerned cylinder, through which the operation of the other cylinders can be continued without being influenced by the concerned cylinder.
The method of diagnosing and controlling combustion according to the present invention is characterized in that flame quenching is judged to have occurred and the fuel injection quantity for the cylinder in which flame quenching is judged to have occurred is increased when the standardized maximum pressure ratio xcex94Pp/xcex94P0 and a standardized combustion pressure ratio xcex94P1/xcex94P0 in the combustion stroke are equal to or smaller than the minimum permissible pressure ratio Pn and permissible pressure ratio Pm of misfire, respectively (i.e., when xcex94Pp/xcex94P0xe2x89xa6Pn and xcex94Pp/xcex94P0xe2x89xa6Pm), and a combustion pressure ratio xcex94P2/xcex94P0 is larger than permissible pressure ratio Pm1.
As the apparatus for effectuating the method of the present invention, the apparatus is composed such that the combustion diagnosis apparatus is provided with a means(step) for outputting a judgement signal of the occurrence of flame quenching in the combustion chamber when the standardized maximum pressure ratio xcex94Pp/xcex94P0 and a standardized combustion pressure ratio xcex94P1/xcex94P0 in the combustion stroke are smaller than the permissible minimum pressure ratio Pn and permissible pressure ratio Pm of flame quenching and at the same time combustion pressure ratio xcex94P2/xcex94P0 is equal to or exceeds the permissible pressure ratio Pm1. The combustion control apparatus is provided with a means(step) for increasing the fuel quantity injected to the cylinder in which flame quenching has occurred upon receipt of the occurrence of flame quenching.
According to the invention, when a diagnosis result has been outputted from the combustion diagnosis apparatus that the standardized maximum pressure ratio xcex94Pp/xcex94P0 and combustion pressure ratio xcex94P1/xcex94P0 are equal to or smaller than permissible minimum pressure ratio Pn and permissible pressure ratio of misfire Pm, respectively, and that the standardized combustion pressure ratio xcex94P2/xcex94P0 is equal to or larger than permissible pressure ratio of flame quenching Pm1, the fuel injection quantity to the concerned cylinder in which flame quenching has occurred or, for example, pilot fuel injection quantity in the case of a gas engine having a sub-combustion chamber to be injected with pilot fuel, is increased. Thus, the occurrence of flame quenching is detected with reliability without delay and measures can be taken to deal with the situation, that is, to increase the quantity of fuel injection to the concerned cylinder, through which the continuation of misfire can be prevented and the operation of the other cylinders can be continued without being influenced by the concerned cylinder.
In the method of the invention, by determining threshold values for diagnosing combustion as a function of engine operating conditions, threshold pressure ratios for diagnosis categories such as permissible maximum cylinder pressure ratio, permissible compression pressure ratio, permissible pressure ratio of knock, misfire, and flame quenching can be changed according to detected engine load, engine rotation speed, inlet air temperature, etc.
Accordingly, the threshold values can be adjusted to match the engine operating conditions, and accurate combustion diagnosis can be effectuated.
It is preferable in the method of diagnosing and controlling combustion according to the present invention that when abnormality is detected concerning a cylinder pressure detector which detects the pressure in a combustion chamber and inputs it to the combustion diagnosis apparatus, the fuel ignition timing of the concerned cylinder of which the cylinder pressure detector is abnormal is retarded by a certain crank angle to a safety position for combustion through a combustion control apparatus which performs combustion control including the controlling of ignition timing and fuel injection quantity. After the pressure detector is recovered by replacement or repair thereof, the combustion control apparatus is allowed to return to normal operation to restore the fuel ignition timing of the concerned cylinder to normal timing.
By the invention, when a diagnosis result has been outputted from the combustion diagnosis apparatus that the cylinder pressure detector is abnormal, the fuel injection timing of the concerned cylinder of which the pressure detector is abnormal is retarded by a certain crank angle to a safety range for combustion while leaving the abnormal state of the pressure detector as it is. After the pressure detector is recovered, the combustion diagnosis apparatus automatically recovers normal operation and allows the combustion control apparatus to operate normally to restore the normal injection timing of the concerned cylinder.
Therefore, when abnormality occurs in a cylinder pressure detector, the pressure detector is repaired or recovered while the injection timing of the concerned cylinder is adjusted to a safe timing for combustion, and after the recovery of the pressure detector, the normal combustion control is recovered, so the abnormal pressure detector can be dealt with without halting the operation of the engine.
The method of diagnosing and controlling combustion of the present invention is characterized in that a plurality of kinds of abnormality are judged in a predetermined crank angle range in the suctionxcx9ccombustion stroke. A condition not sufficient for any one of the kinds of abnormality continues for a predetermined plurality of number of cycles i, the concerned cylinder pressure detector is judged to be abnormal.
Concretely, the steps comprise:
(a) a step for judging whether the detected pressure by the cylinder pressure detector 1 is within the range PTaxcx9cPTb or not during the whole crank angle of one cycle, (b) a step for judging whether the detected pressure is within the range PSb (permissible maximum inlet pressure)xcx9cPsa (permissible minimum inlet pressure) or not in the suction stroke, (c) a step for judging whether crank angle Ppang at the maximum pressure Pp is within the crank angle range corresponding to combustion range Aaxcx9cAb or not, and (d) a step for judging whether the standard deviation Pb"sgr" of Pb""s of past n cycles, Pb being reference pressure at or before the beginning of compression including inlet air pressure, is smaller than a predetermined value xcex5 or not.
(b)
According to the invention, by judging in step (a) whether the detected pressure is within the range PTaxcx9cPTb or not during the whole crank angle of one cycle, the presence or absence of fundamental abnormality in the pressure detector can be judged. In step (b) is judged whether the cylinder pressure in the suction stroke is between the maximum permissible value PSb and minimum permissible value PSa, so the occurrence of drift due to the change-over-time of the detector can be detected in the condition of nearly constant suction pressure. Further, in step (c), as whether the crank angle Ppang at the maximum cylinder pressure is within the crank angle range Aaxcx9cAb corresponding to the combustion range or not is judged, it can be ascertained if the cylinder pressure is detected without deviation in relation to crank angle or not. Further, in step (d), since whether the standard deviation of reference pressure at or before the beginning of compression for a plurality of cycles, the reference pressure being by its nature substantially constant, is within permissible value xcex5 or not, misdiagnosis due to stationary noise can be avoided.
Furthermore, since the pressure detector is judged to be abnormal only after a state in which any one of the conditions (a)xcx9c(d) described above is not satisfied continues to occur for a plurality of times, the influence of instantaneous trigger noise can be neglected.
Therefore, according to the invention, abnormality in the pressure detector is judged through a plurality of detecting methods from various facets. Moreover, the detector is determined to be abnormal only after dubious phenomenon is detected for a plurality of times, so the abnormality can be judged with high accuracy without misjudgment owing to trigger pulse, etc., irrelevant to the abnormality of the pressure detector, resulting in a smooth combustion diagnosis by the elimination of misjudgment.
The present invention is characterized in that there are provided a means (step) for calculating the pressure difference xcex94P between detected cylinder pressure P detected for every crank angle in the combustion crank angle range and the reference pressure Pb at or before the beginning of compression including inlet pressure(xcex94P=Pxe2x88x92Pb). A means(step) calculates standardized cylinder pressure ratio, which is the ratio of the pressure difference xcex94P to the pressure difference xcex94P0, i.e. xcex94P/xcex94P0, xcex94P0 being the pressure difference between the pressure P0 at one or a plurality of predetermined crank angle in the compression stroke and the reference pressure Pb (xcex94P0=(P0xe2x88x92Pb). A combustion diagnosis apparatus is provided with a pressure/analog voltage converting means (step) for outputting at least a part of the result of diagnosis as analog information when diagnosing the condition of combustion such as cylinder pressure condition in the combustion chamber using said standardized cylinder pressure ratio xcex94P/xcex94P0. A combustion control apparatus controls the combustion condition of the engine by reconverting the analog information outputted from the combustion diagnosis apparatus to pressure information. Engine stopping or fuel ignition timing or the injection quantity of the pilot fuel and gas fuel is controlled based on the diagnosis result of the pressure information reconverted from the analog information.
It is suitable that the combustion is diagnosed on the basis of each threshold value determined for each diagnosis category information using the cylinder pressure ratio xcex94P/xcex94P0 in the predetermined combustion crank angle range. To be more specific, it is suitable that the threshold values determined for every diagnosis category information are determined so that the level of each threshold decreases stepwise, and information of a different diagnosis category can be judged at a different threshold level. For example, a pressure detection range is determined near the crank angle of maximum combustion pressure, the threshold for each diagnosis category information is Pp0 and Ph1 for abnormal Pmax, Ph2 for knock, Pn for misfire and flame quenching, and the level of each threshold value is decreased in orderly sequence of Pnxe2x89xa6Ps1xe2x89xa6Pshxe2x89xa6Ph2xe2x89xa6Ph1xe2x89xa6Pp0.
Signals of the result of diagnosis transmitted from the combustion diagnosis apparatus to the combustion control apparatus are composed of analog levels, and each analog level for each diagnosis category is determined to decrease stepwise so that the information of a different category is able to be discriminated by the analog level on the combustion control apparatus side. The analog levels for each of the diagnosis categories are determined so that the level for transmitting the information of diagnosis category of normal combustion state is positioned in the middle of the levels, the levels for transmitting the information of abnormal maximum cylinder pressure or compression pressure, etc., which are generally related to engine conditions as a whole, are set to values in higher level range, and the levels for transmitting the information of misfire, flame quenching, abnormal sensor, a break in wire and so on, which are generally experienced in an individual cylinder, are set to values in lower level range. By determining each level like this, simple and reliable transmission of information is effectuated, and even if an analog level at the transition instant of analog level or erroneous information is read, critical malfunction of the control apparatus is evaded.
To be more specific, it is suitable that each of the analog levels, that is, Cp: the analog level for transmitting abnormal Pmax judgement, Ce: analog level for compression pressure judgement, Ck: analog level for knock judgement, Cq: analog level for flame judgement quenching, Cm: analog level for misfire judgement, and Cx: analog level for abnormal sensor judgement, is determined to decrease stepwise in the orderly sequence of Cp greater than Ce greater than Ck greater than Cq greater than Cm greater than Cx.
It is suitable that, when the range of normal combustion pressure or pressure ratio of each cylinder, the pressure or pressure ratio being between the threshold for knock and that for flame quenching, is transmitted to the combustion control apparatus side at an analog level, the pressure (pressure ratio) is converted to a stepless analog level signal corresponding with the pressure (pressure ratio) and the steplessly controlled analog signal is transmitted to the combustion control apparatus side.
It is also suitable, when applying to a multi-cylinder engine, that a number of analog signal transmission wires corresponding to the number of cylinders are connected between the combustion diagnosis apparatus and combustion control apparatus, the diagnosis result of each category are transmitted in serial order on each analog level determined to decrease stepwise, and the diagnosis category is judged or the combustion pressure or pressure ratio is judged based on the corresponding analog level on the combustion control apparatus side.
A knocking state which has been difficult to detect hitherto can be grasped indirectly by the ratio of pressure differences as a measure, and engine operation near knock limit is always possible, resulting in increased engine efficiency. The combustion diagnosis is not influenced by the change in temperature of the pressure sensor and abnormal combustion and an abnormal pressure sensor such as a broken sensor or a break in a wire can be detected without influence by the drift due to the change over time of the pressure sensor.
The number of signal transmission wires between the combustion diagnosis apparatus and combustion control apparatus is reduced compared with the conventional method of connection. If a break in a wire occurs, the influence thereof is limited only to the concerned cylinder. Besides, the broken wire is able to be identified, which has been impossible with conventional digital signal transmission wires, because the analog value on the wire becomes zero level, which belongs to no category of diagnosis.
By adopting stepless control to effect feedback of the deviation in pressure from the target value of cylinder pressure, more carefully thought out control is possible, resulting in further increased engine efficiency.
For example, a stepless analog level is determined for a normal combustion range in FIG. 23(A) and FIG. 23(B). The data of the result of diagnosis {Ph2xcx9cPn} is converted to analog information {Ckxcx9cCq} to be transmitted as a substitute for the diagnosis result, and it is reconverted to {Ph2xcx9cPn}. By determining a necessary increment or decrement xcex94T of the injection timing for keeping the cylinder pressure ratio in the normal range, the injection timing of each cylinder is properly changed for each cycle.
The present invention is characterized in having a display apparatus for representing detected cylinder pressure-crank angle curve inputted to the combustion diagnosis apparatus. The display apparatus comprise a first ring memory provided on the diagnosis apparatus side for memorizing the cam top crank angle of a reference cam and the cylinder pressure-crank angle curve, and a second ring memory provided on the display apparatus side for memorizing the cylinder pressure-crank angle curve in a certain crank angle range of each cylinder and a display. The first ring memory on the diagnosis side has a means (step) to start the program by an interrupt of the signal from the crank angle detector after the detection of the cam top crank angle of the reference cam and write in the cylinder pressure wave form, which indicates combustion condition, at a certain interval of crank angle to the ring memory in the determined area corresponding to each cylinder. The pressure-crank angle curves of all cylinders are read out from the determined area of the second ring memory and these pressure curves are displayed on the display with the pressure curves shifted so that each curve does not overlap.
It is suitable that the cylinder pressure-crank angle curves of all cylinders are written into the first ring memory on the diagnosis apparatus side in synchronization with the crank angle at the moment-to-moment detection of the pressure with the cylinder pressure detector (sensor). On the other hand, the cylinder pressure-crank angle curves of all cylinders are written in the second ring memory after the cam top crank angle of the next cycle after the previous cycle(720xc2x0) is completed, is detected, and the memorized pressure curves are represented on the display.
According to the invention, visualization of combustion condition changing moment-to-moment is possible on an oscilloscope (display), and the cylinder pressure-crank angle data overlapped with regard to time is easily recognizable. It becomes possible to observe pressure curves of a plurality of cylinders by transmitting the data to the display apparatus in serial order while diagnosing combustion.